1. The Field of the Invention
This invention relates to communication systems that are used by computer equipment to communicate data across public or private telephone lines. More particularly, the invention relates to a system and method for connecting and interfacing a communications device to a telephone line via a telephone set.
2. The Relevant Technology
Increasingly, users of personal computers and related equipment rely on the ability to utilize public and private telephone lines to transmit and receive data. This capability dramatically increases the value and usefulness of the computer, as well as the overall productivity of the computer user. As the availability of personal communications equipment, remotely accessible public and private networks, databases, computer-based bulletin boards and related computer services continues to increase, the need to have reliable and consistent access to telephone communication links will continue to grow.
As is well known, equipment such as personal computers and facsimile machines communicate across telephone lines via a piece of equipment known as a "modem." The term modem is an acronym derived from the phrase "modulator-demodulator," which is descriptive of the basic function performed by the modem. A modem enables digital equipment to interface with the public telephone network, which is designed to carry analog type "voice" signals. The modem accomplishes this by modulating the outgoing digital data so that it is compatible with the analog signal format used by the telephone network. Similarly, the modem reverses the process by demodulating incoming analog signals from the telephone network into the digital signal format that is compatible with most computer equipment.
The standard telephone line, whether public or private, utilizes a two-wire communication path--wherein one wire forms a transmission path and the other forms a receive path. Similarly, most communication devices, including modems and telephone sets, have a two-wire transmit path and a receive path that corresponds with the two-wire telephone line. Ideally, the transmit wire and the receive wire of the communication device (often referred to as the "tip" and the "ring" lines) are connected directly to the corresponding two wires of the telephone line via a RJ-type module and plug/cable detachable interface arrangement. However, under many circumstances such a direct interface is either impractical, inconvenient and/or not physically or electrically possible.
Typically, a communication device such as a personal computer modem, does not have access to a separate and dedicated phone line reserved solely for data communications. This is especially true in telephone systems which utilize a central Private Branch Exchange (PBX), where many telephone lines are serviced by a central PBX controller. In such an arrangement, which is common in many offices, hotels, schools and similar buildings, the telephone equipment is not connected directly to the public telephone network. Rather, the PBX acts as an automatic switching system to interconnect communication devices, such as telephone sets, within a building or campus of buildings. When communication is required outside of the building, the PBX acts as a multiplexing gateway to the public telephone network. Consequently, the providing of dedicated telephone lines for modems is often an impractical and inefficient use of a PBX system, and could result in a need for additional public telephone lines that may not be used to fill capacity.
Thus, in a typical telephone environment, a user may desire to have both voice and data communication capabilities over a single telephone line. Often however, it is difficult to share a line between a modem and a telephone set. For instance, in many PBX systems a telephone set, specifically designed for use with the particular PBX controller, must always be coupled to the telephone line. Decoupling of the telephone set from the line may disrupt the PBX controller and thereby prevent proper line selection for outgoing communications. As such, a user cannot simply unplug the telephone set from the phone jack and plug in the computer modem to access the public telephone network.
Also, some PBX systems may utilize modular phone jacks that are not of a conventional size and/or shape, or which utilize a different electrical interface. Often, such an arrangement will not be compatible with the standard RJ-type connector found on many modems, and the user cannot physically and/or electrically interconnect with the telephone line. A similar problem occurs when there is not a modular wall/jack connector available to the modem user. For instance, some office buildings and many hotel rooms have telephone sets that are hard-wired directly into the telephone line, rather than via a RJ-type modular plug and jack arrangement Again, the modem cannot be physically interconnected with the telephone line, and it is therefore rendered useless.
Even in those instances where a single telephone line can be used both for both voice and data transmissions, the line must be physically shared between the telephone set and the modem. Under this arrangement, the telephone set must be physically disconnected from the telephone line in order to connect the modem, and vice-versa. This process is time consuming, awkward and inefficient, and does not allow an effective or efficient sharing of the single phone line.
It will be appreciated that the above problems to gaining access to the telephone network can prevent the effective use of any communication device. However, such difficulties are especially problematic for the increasing number of users of portable computers (referred to variously as laptop, notebook, subnotebook or palm-top computers), for whom the ability to access the public telephone network is extremely important. These types of personal computers are often equipped with internal modem and facsimile devices, and, due to their mobility, must be capable of accessing telephone lines under a wide variety of circumstances--including those discussed above.
Solutions to the problems encountered when attempting to access the public telephone network for data communications have heretofore not been entirely satisfactory. As mentioned above, in the typical telephone set the telephone base uses a two-wire communications connection that is coupled directly to the two-wire telephone line. The telephone set also includes a handset, which is coupled to the telephone base via a handset cord. Usually, the handset cord has a modular RJ-type plug at one end, which detachably mates with a handset jack mounted in the telephone base. The telephone base includes circuitry that converts incoming and outgoing signals from the two-wire telephone line connection to a four-wire connection at the handset jack. This is because the wiring between the base and the handset includes a pair of microphone lines (i.e., a pair of transmitting lines) and a pair of speaker lines (i.e., a pair of receiving lines), which collectively couple the base hardware to a microphone and speaker mounted in the handset.
Given this standard arrangement, one solution to the above mentioned problems has been to provide an interface adapter that allows the modem to connect to the telephone line via the telephone set. Under this approach, the telephone base remains interconnected with the two-wire phone line, and the modem connects, via the adapter, to the handset jack mounted in the telephone base. The handset and handset cord are also connected to the adapter, and the user may, by operating a switch on the adapter, use the phone line for voice or data communications.
However, when in a data communication mode, the adapters of this sort must include conversion circuitry that interfaces the two wires of the modem with the four wires of the telephone handset jack--essentially duplicating the function already performed in the telephone base. Consequently, these adapters require additional circuit components and an independent power supply, thereby resulting in an adapter which has a higher overall cost. Further, to accommodate the additional conversion circuitry, the adapter is necessarily larger and bulkier--a characteristic that is particularly inconvenient to users of portable computers.
In addition, the prior art adapters allow a modem to connect to any one of many different types of telephone sets. As such, the adapters include circuitry that regulates the voltage level of the transmit signal (i.e., the "volume" of the signal) that is generated by the modem and supplied to the telephone base. This is done to avoid problems such as feedback, signal distortion and signal loss, and to insure that the data signals generated by the modem are accurately transferred to the telephone line after passing trough the telephone base. This voltage level is typically adjusted by way of a manual switch and circuit arrangement. Again, this approach necessarily results in a costlier, more complex, and physically larger adapter. Further, manual adjustment of the transmit signal amplitude may not be sufficiently precise, and could potentially result in loss of data--especially at the high transmission speeds of today's modems.
Finally, in order to establish a data communications link with adapters of this type, a precise sequence must be followed by the modem user. Typically, the user must first insure that adapter is properly connected to the computer modem and then set the transmit "volume" level to one that corresponds with the type of telephone set being used. The user must then remove the handset from the phone base cradle and listen for a dial tone. The user must then immediately cause the modem to dial a phone number, or risk losing the dial tone. If the sequence is deviated from at any step, the modem will not be able to establish a communication link, and the process must be repeated. As will be appreciated, this approach can be confusing to many modem users, and often is the source of error when attempting to establish a data communication link.